There exists a technique for accurately finding the number of people who enters into and exits from a building or a room.
For example, Patent Literature 1 discloses an invention in which a television camera is installed to capture an image around a door and detect entry into a room and detect exit out of a room from a change in the captured image. In this invention, a human body is detected from a captured image, and entry into and exit out of the room is detected from the direction of the passage, so that the number of people passing through the monitoring area is counted.
Patent Literature 2 discloses a system including two person-detection sensors provided along the travelling direction of an aisle around a doorway, and detecting a person who enters into the room or exits out of the room from a time difference of detection signals detected by the two person-detection sensors. This system determines that a person (human) moves in a direction from a person-detection sensor reacted first to a person-detection sensor reacted later.
Patent Literature 3 discloses an invention for detecting room entry and exit by using person detection sensors installed in a doorway at the inside and the outside of the room and an auxiliary sensor installed at the side of the door to detect a transition body. This invention detects a person who enters into the room or a person who exits out of the room in accordance with the order of reactions of the three sensors. In this invention, the auxiliary sensor is used to prevent false detection caused by a movement of a person who does not pass through the door, and this invention achieves a higher level of detection of room entry and exit than the invention disclosed by Patent Literature 2.